1. Field of the Invention
The present invention generally relates to the design and use of implantable medical devices, and in particular to the design and use of an implantable device for establishing long-term access to a patient's blood circulation for extra corporeal treatment of blood, such as hemodialysis, hemofiltration, oxygenation of blood and other.
2. Present State of Art
Despite several types of vascular access ports and devices proposed over recent years, vascular access remains one of the most problematic areas in treatment of patients requiring long-term access to their vascular system, such as hemodialysis. Almost all of those patients undergo a placement of one of the two, or both of widely accepted long-term vascular access options, during the life of their hemodialysis treatment. The first one is a surgical placement of an arteriovenous synthetic graft connecting patient's adjacent peripheral artery and vein to divert some of the arterial blood flow through the graft. The other is an arteriovenous fistula, a direct surgical connection between adjacent artery and vein with no synthetic conduit used. In both cases the blood circulation is accessed with two needles inserted though the skin either into the synthetic graph in the former case, or into the venous portion of an arteriovenous fistula in the latter scenario. This is done during each hemodialysis session in order to circulate blood through the dialysis machine and back into the patient. When artery is connected to a vein directly or through a synthetic graft, low-pressure low oxygen venous system is subjected to high pressure oxygenated arterial blood. Those conditions lead to a significant turbulence and damage of the vascular endothelium (cellular lining) on the venous side with subsequent narrowing of the vascular lumen, decrease of the flow in the access site and almost invariable occlusion of the established access. Needle stick injuries and infections also contribute to the loss of those types of accesses. As a result more than 60% of the synthetic grafts fail in the first year of use and nearly all of the remaining grafts fail in the second year. Arteriovenous fistulas have longer survival rates, but still very short of a desirable lifetime. Surgical intervention is warranted to reestablish the access each time it is occluded. Consequently, maintenance of vascular access for dialysis became a formidable and extremely costly obstacle in delivering lifesaving treatment for dialysis patients. More importantly, running out of vessels available for surgical access leaves no treatment options for some patients.
Several ports and access devices have been proposed over the recent years to address the significant shortcomings of the traditional vascular access types. However even though some of the solutions offer theoretical advantages over the traditional vascular accesses, none of the solutions found widespread application as treatment modalities either due to their inability to offer any practical advantages to existing solutions, or their prohibitively high rate of complications, mostly infections and clogging of the access. Thus creating an alternative vascular access for a long-term extra corporeal treatment of blood remains an extremely important task.
Long-term implantable vascular access solutions can be divided on subcutaneous, when an access port is implanted under the level of the skin, and percutaneous, when the access part is of the port is placed above the level of the skin to be accessed without the skin penetration. Presently available subcutaneous ports usually consist of a metal or synthetic housing which contains an access chamber and some type of a valve or a high-density, self-sealing septum, made of silicone rubber or similar material, which separates the access chamber from a conduit connecting the access port to a vein or other internal fluid conduit or cavity. The circulation is then accessed by the needle(s) inserted through the skin into the valve mechanism or through the septum to have a direct communication with the conduit(s) connecting the chamber with the blood vessel. After the blood treatment session the access is flushed with some type of the solution to prevent blood clotting and infection in the conduit.
Example of such a device is disclosed in a series of U.S. patents all titled “Implantable Access Devices” and issued to Ensminger et al. (U.S. Pat. Nos. 5,180,365 (Jan. 19, 1993), U.S. Pat. No. 5,226,879 (Jul. 13, 1993), U.S. Pat. No. 5,263,930 (Nov. 23, 1993), U.S. Pat. No. 5,281,199 (Jan. 25, 1994), U.S. Pat. No. 5,503,630 (Apr. 2, 1996), U.S. Pat. No. 5,350,360 (Sep. 27, 1994), U.S. Pat. No. 5,417,656 (May 23, 1995), U.S. Pat. No. 5,476,451 (Dec. 19, 1995), U.S. Pat. No. 5,520,643 May 28, 1996, 5,527,277 (Jun. 18, 1996), U.S. Pat. No. 5,527,278 (Jun. 18, 1996) U.S. Pat. No. 5,531,684 (Jul. 2, 1996), U.S. Pat. No. 5,542,923 (Aug. 6, 1996), U.S. Pat. No. 5,554,117 (Sep. 10, 1996), U.S. Pat. No. 5,556,381 (Sep. 17, 1996), U.S. Pat. No. 5,792,123 (Aug. 11, 1998). Another example of subcutaneous port is marketed by Vasca, Inc. (U.S. Pat. No. 5,713,859 (Feb. 3, 1998), U.S. Pat. No. 5,755,780 (May 26, 1998), U.S. Pat. No. 5,931,829 (Aug. 3, 1999), U.S. Pat. No. 6,007,516 (Dec. 28, 1999), U.S. Pat. No. 6,042,569 (Mar. 28, 2000), U.S. Pat. No. 6,238,369 (May 29, 2001) U.S. Pat. No. 6,056,717 (May 2, 2000), U.S. Pat. No. 6,258,079 (Jul. 10, 2001)) and Biolink's Dialock system (U.S. Pat. Nos. 5,954,691 (Sep. 21, 1999), U.S. Pat. No. 6,206,851 (Mar. 27, 2001), U.S. Pat. No. 6,506,182 (Jan. 14, 2003)).
All of the above and similar solutions share some significant limitations that prevent widespread use of those devices. Those devices represent an improved version of regular indwelling catheters and inherit many of the complications associated with the use of the latter. An implanted catheter usually has to be placed in a central vein to achieve acceptable flow rates. Such placement creates conditions such as low-flow state and disruption of a laminar flow which known to be the cause of infection and thrombosis. In addition implanted catheter inserted or attached to a central vein is difficult to vigorously disinfect, which increases the risk of infection in the catheter. Moreover, the central vs. peripheral placement of those devices not only provides a higher risk of serious infectious complications such as endocarditic, but also makes it much more difficult to diagnose early signs of those complications. Recent improvements in battling the infection in those devices might make some of them a useful treatment option in limited number of patients, but they are unlikely to provide adequate long-term vascular access in the majority of rapidly growing number of patients requiring regular access to their circulation for many years.
Percutaneous catheters have an external port coming out of the skin of the patient, which eliminates the necessity of using needle sticks to access the vascular system. Hemapure U.S. Pat. No. 6,436,089 proposed Hemaport, a percutaneous port that provides a mechanism for needle-less access to a synthetic graft, connecting patient's peripheral artery and vein, similar to the traditional arteriovenous graft. Although addressing one of the disadvantages of the traditional access, needle puncture of the skin and the vessel, the design inherits all the other shortcomings of arteriovenous graft responsible for it's failures. In addition a percutaneous portion of any device is always subject to a higher risk of infection that prevented use of various types of ports over years. Hemaport design is not offering anything to suggest that the device will have any different fate in that regard than previous solutions, which in addition to inherited problems of a conventional arteriovenous graft makes it's practical use highly improbable.
Another variant of percutaneous device is described in U.S. Pat. No. 5,147,321. The device is a percutaneous rotation switch mechanism, which consists of a hollow metal cylinder with one end of it perpendicularly attached to the middle portion of another tubular conduit with two round openings connecting the two cavities, with another end being a part of a percutaneous portion of the device to provide a direct access to the lumen of the second conduit through the cavity of the first one. A tightly fit solid cylinder with two parallel longitudinal channels is placed inside the first cylinder and can be rotated 90° to switch between two positions. The first “ON” position is when the two channels are aligned to the two openings to create two conduits going through the first cylinder into the cavity of the second one. The second “OFF” position is when the channels are not aligned to the openings closing the lumen of the second cylinder off. During implantation a vascular graft or any other blood vessel is transversally cut and the second cylinder is placed between the split ends to align the lumen of the cylinder with the vascular lumen in a continuous fashion. When the switch is in “ON” position two parallel channels are established between extra corporeal space and the vascular lumen, providing the route for withdrawal and returning blood back to the circulation. By rotating the internal cylinder 90° to the OFF position the channels are not aligned to the openings closing the vascular lumen off. Although this design eliminates the necessity of needle sticks it has major limitations. It designed to be inserted in arteriovenous graft thereby it would retain all of the limitations of the traditional graft. More importantly, the openings connecting the channels to the vascular lumen are positioned closely to each other allowing for a significant recirculation, especially in low-pressure systems (if placed into the venous system), thereby making the treatment of the blood very inefficient.
None of the prior art devices provides the solution for identified problems with existing vascular accesses. In summary it is desirable to provide a device that would address all of the following issues:                1. Eliminate or reduce factors that lead to narrowing and occlusion of the access.        2. Provide an effective mechanism to prevent or decrease infections associated with the use of the device.        3. Provide sufficient blow flow rates for extra corporeal treatments, such as dialysis        4. Eliminate the necessity of the needle puncture of the skin and the device to ensure no long-term damage to the vessel or device.        5. Provide a better patient comfort with resulting improved patient compliance.        6. Ensure safety, robustness and easiness of use of the device        